The present invention relates to a graft copolymer having a molecular structure consisting of a carbon-carbon backbone chain structure and grafting units thereon derived from an organopolysiloxane. More particularly, the invention relates to an organopolysiloxane-grafted organic polymer free from aliphatic unsaturation and safe from the troubles due to emission of an offensive or irritative odour and low storage stability as well as to an improved method for the preparation of such an organopolysiloxane residue-grafted copolymer.
Graft copolymers consisting of a backbone moiety of an organopolysiloxane and grafting moiety derived from an organic polymer are well known in the prior art. For example, the hydrosilation reaction between an organopolysiloxane having silicon-bonded hydrogen atoms and an alkenyl-terminated polyoxyalkylene compound in the presence of a platinum catalyst leads to a graft copolymer of which the backbone moiety is derived from the organopolysiloxane molecules and the grafting moiety consists of the polyoxyalkylene residues. Such a graft copolymer is usually referred to as a polyoxyalkylene-modified or polyether-modified organopolysiloxane.
A serious problem in such polyoxyalkylene-modified organopolysiloxanes in general is that, since the hydrosilation reaction cannot proceed to completeness, the reaction product more or less contains a small amount of the unreacted alkenyl-containing polyoxyalkylene compound or an impurity by-product compound formed by the intramolecular rearrangement reaction thereof which is responsible for the emission of an offensive odour. The polyoxyalkylene molecules per se are susceptible to an oxidative degradation reaction to produce an aldehyde compound which is also very offensively odorous.
With an object to solve this problem due to emission of an offensive odour from a polyoxyalkylene-modified organopolysiloxane, a proposal is made in U.S. Pat. No. 5,225,509 and Japanese Patent Kokai 7-330907 according to which the reaction mixture after the hydrosilation reaction is subjected to a hydrogenation reaction to effect deodorization by the hydrogenating reduction of the alkenyl groups and prevention of oxidative degradation of the polyoxyalkylene groups.
Apart from the above described polyoxyalkylene-modified or ganopolysiloxanes as a graft copolymer, organopolysiloxane-grafted organic polymer-based graft copolymers are also disclosed in Japanese Patent Kokai 58-154766, 59-20360, 59-126478, 61-151972 and 62-156172 and elsewhere. As compared with the above described polyoxyalkylene-modified organopolysiloxanes, the organopolysiloxane-grafted copolymers have excellent weatherability, water-repellency, anti-stain insusceptibility, surface releasability, lubricity and other properties so that proposals are made for the application of these graft copolymers as an adjuvant in a variety of coating compositions. In particular, proposals are made in recent years in Japanese Patent Kokai 5-339125, 6-9332, 6-279232, 7-187951, 7-137954, 7-196449, 8-143427 and 9-296134 and elsewhere for the use of the organopolysiloxane-grafted copolymer as an additive ingredient in cosmetic and toiletry preparations.
The most typical method for the preparation of an organopolysiloxane-grafted organic graft copolymer is a radical copolymerization reaction of a macromolecular organopolysiloxane compound having a radical-polymerizable terminal group at a single molecular chain end as a grafting unit-containing comonomer with an organic radical-polymerizable monomeric compound or compounds to form the carbon-carbon backbone chain structure of the graft copolymer so as to introduce the organopolysiloxane residues as the grafting units onto the backbone chain structure. Since the copolymerization reaction is conducted in most cases with a (meth)acrylic group-containing monomeric compound as the organic comonomer for the backbone structure and a (meth)acryloxyalkyl group-terminated organopolysiloxane as the grafting unit-introducing comonomer, it is sometimes the case that a strongly irritative odour is emitted from the graft copolymer obtained by the copolymerization reaction. The irritative odour in this case is much more offensive than the aldehydic odour emitted from the polyoxyalkylene-modified organopolysiloxanes. When the organopolysiloxane-grafted copolymer contains a substantial amount of unreacted (meth)acrylic monomers, moreover, the graft copolymer product cannot be fully stable in storage and cannot be free from the problem of safety due to the high radical-reactivity of the (meth)acrylic groups so that application fields of the graft copolymers for commercial products are necessarily limited despite the so large possibility of applications and the great demand from the commercial market for the graft copolymer products.